Inequalities and indoor air pollution: a prospective observational study of particulate matter (PM2.5) levels in 309 UK homes from the Born in Bradford cohort study

Particulate matter (PM2.5) is associated with substantial morbidity and mortality. Evidence suggests socioeconomic and ethnic minority groups are disproportionately exposed to higher outdoor air pollution, exacerbating existing health inequalities. However, most research focuses on outdoor air pollution, despite people spending most of their time indoors. We compare how indoor PM2.5 concentrations vary between households of different socioeconomic status and ethnicity, and test for associations with asthma-related symptoms. We recruited 321 households from the multi-ethnic Born in Bradford cohort. Low-cost commercial sensors sampled PM2.5 in three rooms over a two-week period. Information on socio-economic status, home and building characteristics, and asthma related symptoms were collected for 309 mothers and 293 children. We calculated metrics for indoor PM2.5 concentration (µg/m3) to compare with current guideline thresholds and to capture peak events that might be important for health symptoms. We investigated whether PM2.5 concentrations varied by key sociodemographic and home characteristics. Logistic regressions examined whether PM2.5 metrics predicted asthma-related symptom occurrence for mothers and children, controlling for covariates. Homes had a mean daily average indoor PM2.5 concentration of 20.2 µg/m3, exceeded the WHO 24-hour threshold an average of 41% monitored days, and exceeded 100 µg/m3 an average of 4% monitored hours. South Asian homes had higher PM2.5 concentration than White British or Other ethnicity homes (23.5 µg/m3, 17.1 µg/m3, and 16.5 µg/m3 respectively). Higher PM2.5 was observed with higher deprivation levels (most deprived, 24.0 µg/m3, least deprived, 12.7 µg/m3). Higher PM2.5 levels were seen in rented versus owned homes, smoking versus non-smoking households, terraced and semi-detached versus detached homes, and gas versus electric cooking appliances. We did not find clear associations between asthma-related symptoms and PM2.5 metrics. The high indoor PM2.5 levels recorded in homes indicate an urgent need to tackle indoor air pollution as a health risk factor, particularly in deprived and minority ethnic households. Policy action should focus on launching national public awareness campaigns, supporting transition to cleaner cooking and air cleaning technologies, and addressing socioeconomic disparities related to high indoor air pollution.